This invention relates to a plating solution automatic control method, and more particularly, to such an automatic control method useful in controlling electroless plating solutions and electroplating solutions.
Some prior art known methods for the automatic control of an electroless plating solution involve automatically analyzing the concentration of a consumable ingredient in the solution. When the result of analysis shows that the concentration of the consumable ingredient in the solution is below a predetermined level, a necessary amount of a replenisher is automatically supplied to the solution to restore the concentration to the predetermined level.
This type of plating solution automatic control method includes the steps of sampling the plating solution, thereafter analyzing the sample to determine the concentration of a consumable ingredient, detecting from the result of analysis whether or not the concentration is reduced below the predetermined level, and supplying a necessary amount of replenisher to the solution. Thus there is a time lag between the sampling and the replenishment. Consequently, a substantial difference sometimes occurs between the concentrations of the consumable ingredient in the solution at the time of sampling and at the time of supplying the replenisher. The latter concentration can be considerably lower than the former concentration. Under such circumstances, the supply of replenisher which is determined on the basis of the concentration of the consumable ingredient in the solution at the time of sampling will not be sufficient to adjust the concentration of the consumable ingredient to the predetermined level. The time lag from sampling to replenisher supply is increased when the analysis technique used is a titration using a chemical reagent. The time lag, the difference between concentrations of the consumable ingredient at the times of sampling and replenisher supply due to such a time lag, and the insufficient adjustment in that the supply of replenisher does not adjust the concentration to the predetermined level because of such a concentration difference are problems encountered in strictly controlling the plating solution concentration within a narrow range for the purpose of producing plating films with consistent physical properties at a constant plating speed.
Such problems arise not only in electroless plating processes, but also in electroplating processes, particularly high speed electroplating processes accompanying rapid ingredient consumption and electroplating processes using insoluble anodes.